Method of manufacturing heat resistant sintered articles



Sept. 16, 1958 c. a. GOETZEL EIAL 7 METHOD OF MANUFAbTURING HEAT RESISTANT SINTERED ARTICLES Filed Aug; 27, 1954 'FIG. I

FIG. 2.

INVENTORS Claus G. Goetzel, Nicholas JG'ran. t Jizclf Rl ofizin 8 Leaner P J/i ZniCi i ATTORN EY METHOD OF MANUFACTURING HEAT RESISTAN T .SINTERED. ARTICLES .Claus G. Goetzel, Yonkers, N- .Yo, NicholasJ. Grant,

Winchester, Mass, and Jack A; Yoblin,Bronx,,and 'Leonard P. Skolnick, New York,fN. 'Y.,..assignors to Sintercast Corporation of America, YonkersyN. Y., a corporation -of N ewYork Application. August27; 1 95,4, Serial .No.; 452,595 -5 Claims. (Cl. 75-201) The present invention relates to heat resistantmetal products and ,more particularly to a reinforced heat resistant metal product capable of sustaining highstren gth properties .and high resistance. to. creepateleyatedtieinperatures above 800 C. and.up to,9 5 0C. and higher ,for prolonged periods of time. i l

Itis wellknown that,considerableprogress has been made in recent years in the development, of wrought nickeland cobalt-base fsuper-alloys.for useinthepro- Auction of powerplant components tor high powered thermal engines such as turbines, rockets, jets, and;the ,like. While these alloys have .added measnr ably to the .scientific development of such 1ettgi lq ncreased h ating temperatures of themorerecently deyelo ernal engines to improve their power ratinghaye plaee cohsiderable burden on t hese.,alloys. It was;found hat these alloys-had definite temperature limitations;. ;in-,.tliat ,they tended to soften and. creep appreciablyat, temperaturesabove 900 C.

.The typical wrought super-alloy general-1y cemprises a wrought solidsolution alloy containing chromium-and ,at .least one metal of. the iron .group as essentiahalloying ingredients together with hardening elements -..to stiffen the alloyfor use at high'ternperatures. Generally,'the stiffening may be achieved in several ways; (1 by1-hardening. the.1solid solution matrix by employing suchrnatrix hardening elements .as molybdenum, tungsten, columtbium, etc., (2) by employing specialelements capable ;of ,forming compounds of low solubility vwhich precipitationharden the. alloy, for example titanium,.aluminum, zir- .conium, .etc .,-(.3) by employingpth'er.elements ,which form awsecond phase upon .solidificationlwhieh hardens .the alloy, etc. The hardening by the secondgrnethod is achieved by heattreatment and may beaernployedsto augment. the hardening fthe firstmethod. Generally, most of the wrought super-alloys .arersusceptible..to.precipitation hardening. The precipitation.hardening.elements in the alloy are taken into solid, solution by heating tliealloy to ahigh solution{.temperature, ior,,example .1000 C.,t o-1250 C., followed. byrapidcoaling to.keep the precipitation hardening .elemen ts in solution. The precipitation hardening is then achieved by. reheating. the lalloy at a lower temperature, for example ,within the range of about 550 C. to 85.0.C.,,f or -a time suflicient "reproduce a critical dispersion of a fine;.p recipitate throughout thev matrix which is generally .inyisib1e,;eyen at a. magnification of 2000 times and higher-.whemaehieving. maximum benefit. Such alloysin thez-hard infld con- Idition exhibit improvedmesistanceato creep at -elevated service temperatures 11p.to,.about..-900. C.. .Howeyer, ,at highertemperatures, the alloys tend toso ftentd ne to two effects. If the service temperature is in the neighborhood of about 850 to 900 C. and,slightly higher, the. a1loys tend to soften due to over-aging. This" phenomengn; is

believed to be due to, a coalescence of thefineprecipitate to' large, coarse particles which is generally accompanied by a falling off in hardness and hence lower 'resistance" to creep. Moreover, when the service temperature is in the 2,852,367 Patented Sept. 16,

neighborhood of -1000 C. to 1100 C. and higher, the precipitate begins to go into solid solution and the alloy bersof thermalengines must be kept ;.extr emely,small, .anyvariation from normal creep canbe. dangerous and lead to serious damage of the powerplant even to-the eatentwhere the. whole engine may be temporarily. stalled 0r possiblytotallydestroyed.

nanv attempt to overcome the foregoing ditficulties, ;.super.-alloys. were proposed with higher amounts. of hardening elements, e. g, carbon, tofurther stiffen them-so ,as to increase their sustaining power at elevated temperat ures. While this washelpful to a-certainextent, the

stiffened alloys generally had lower ductility which was accompanied by a low resistance to impact. ;Moreover, the alloys could-not be worked easily and general-ly were subject to cracking during the hot working operations.

This was especially true when the super-alloys contained particularly high amounts'of matrinhardening elements,

-.p .ec p a :ha e ng l ment w u h-as; titamfimmal m mum, zi o i m, t made to; overcome the; foregoing :difiiculties, none,;. as: far {as .we are, aware, was entirely; successful when }carried 1 into, practice commercially.

Although ,many -.a.t temp.ts were .we; have now diseovered that-heat resistant super-alloys with; improved sustaining power at elevated temperature,

vespecially sustained resistanceto creep atelevated temperatures, well above,800 C. and. even above :950 "C .or 1000 'C., in combination withhigh 'resistancedo impact, can be produced by -employing substantial amounts of a hardening constituent which would normally .embrittle .the alloy. 'By employing .the hardening constituent .in .a special mannen'thealloys of the invention are capable. of maintaining their. stitfnessat elevated tem- /peratures'which normally cause similar alloys outside the :invention to soften and creep substantially.

tIt is the object of the present invention to overcome the limitations inherent in the presently available heat resistant nickel-and cobalt-base alloysand thereby prod-ucean entirely new type of material which combines "high melting point and being characterized by a low degree of solubility in thesolid solution matrix of the heat resistant alloy in which it is contained. The com- -pound also behaves as a recovery inhibitor,-that is, it acts as a deterrent to recrystallization and to abnormal grain growth. {The compound is stable and does not decomfpose'substantially at elevated temperatures and, when uni- -forrnly;d ispersed throughout the matrix of a-heat resistantanoy he alloy is capable of sustaining its mechanical propertiesfor prolonged periods of time at elevated temperatures that normally cause similar heat resistant alloys "to soften-and creep appreciably. It is essential'that the .alloywith the slip and recoyery inhibitor-be produced by powder metallurgy as ordinary melting techniques war not 1 produce the results of the invention. Compounds suitable slip and recovery inhibitors be slightly "soluble so that they will bond securely with the matrix alloy, otherwise if the inhibitors have no solubility in the matrix alloy,

poor bonding results which gives rise to internal cracks and structural defects under stress during fabrication or use. Excessive solubility, on the other hand, tends to decrease the stability of the entire structure at elevated temperatures, leading to a gradual reduction in service,

life due to coalescence of and consequent reduction in the effectiveness of the slip and recovery inhibiting phase.

'The slip inhibitors contemplated comprise mainly the carbides, borides, silicides and nitrides of titanium, zirconium,

columbium, tantalum, hafnium and vanadium, and also the disilicides of molybdenum and tungsten.

In carrying the invention into practice, the hard phase is employed in amounts ranging from about to 20% by'volume, substantially the balance by volume being the heat resistant matrix alloy.

The heat resistant matrix alloy contemplated by the i invention comprises about 5 to 30% by weight of chromium and up to about 25% by weight of iron, substantially the balance of the alloy being at least one metal selected from the group consisting of up to about 90% nickel and up to about 70% cobalt, the sum of the nickel and cobalt contents being at least about 40% of the total alloy composition and preferably at least 50%.

The expressions substantially the balance or balance orremainder? as employed herein do not exclude the presence of' other elements in amounts which do not adversely affect the basic characteristics of the alloy. Thus,

the heat resistant matrix alloy may contain, in addition to chromium, either tungsten or molybdenum, or both, in amounts not inconsistent with forming a substantially ductile matrix. This is also true for other elements which may be present such as columbium, tantalum, titanium, aluminum, etc., provided these and the other elements are not present'in amounts that produce phases detrimental to. the properties ofthe alloy, such as the brittle sigma phase:in chromium-bearing alloys or other phases. As'those skilled in the art will readily understand, small amounts of .other elements may be present either incidentally or as regular additions such as manganese, silicon, boron, etc. .With respectto the carbon and nitrogen contents, these-elementsgenerally do not exceed about 0.25% and about 0.1%, respectively, and preferably should be maintained as low as possible.

Inproducingreinforced heat resistant metal products I in accordance with the invention, the finely divided slip and recovery inhibitor cornpound is mixed with the finely divided heat resistant matrix metal and shaped to a desired configuration which may be accomplished by pressing the powder mixture inja die mold by employing a pressure varying from about30 to 150 tons per square inch. The

resulting body is then sintered at an elevated temperature to consolidate it sufliciently so it can be subsequently hot worked. Generally, the sintering is conducted at a temperature of at least about 1100 C. but not exceeding about 5 below the point of incipient fusion at a subatrnicrons and preferably not exceeding about 50 microns.

7 It is preferred that the sintering be carried out in two When employing the second stage of sintering, it is pre- ;ferred that a subatmospheric pressure not exceeding about 0.1 micron be employed. The sintered body is then hotworked, for example by hot extrusion, forging, swaging, etc., until its cross-section has been reduced at least 50% and preferably at least 90% to 9 5% so that subproportion. Since it is important that the powder be titanium carbide as the slip inhibitor phase, the weight" square inch). The ingots are then sintered in two stages,\

nearly as possible that of the solid body. Thetreatment .mospheric pressure generally not exceeding about 100 two or even one micron in particle size. When a cornmatrix' metal powder and 5-20% by volume ofi'th position comprising about 90% by weight of the nickel cross-section to producea material having not more than 4 stantially all of the voids have been eliminated after which the hot worked body is fabricated into the finished product.

As has been pointed out hereinbefore, it is essential. that powder metallurgy be employed in producing the: reinforced metal product of the invention. In order to obtain a satisfactory dispersion of the hard phase in the; relatively soft matrix, it is necessary that thebase or matrix metal be employed as a fine powder, the maximum particle size not exceeding 40 microns and preferably not exceeding 5 microns, whereas the slip and recoveryfj inhibitor phase should be of even finer particle size, e. g. not exceeding 10 microns, and preferably not exceeding mercialnickel-chromium alloy comprised of about nickel and 20% chromium is employed as the matrix, the fine powder can be obtained by mechanical comminution or milling the alloy, or preferably by the reduction of nickel and chromium oxide powder mixtures in the proper p as free from oxygen as possible, r'eductionof the oxide mixture by the hydride process is preferred. As for'tlre hard slip and recovery inhibitor phase, e. g. titanium car bide, the ultra-fine powder can be obtained by prolonged ball milling in carbide-lined ball mills,'using cemented tungsten carbide balls. Milling times are preferably in the order of 120 hours and in a medium such as xylene trichlorethylene. or carbon tetrachloride. The two powdered ingredients are blended in a" vol umetric proportion of from 8095% of the relatively soft? ultra-fine hard slip inhibitor powder. "When the 80-20, nickel-chromium base or matrix alloy is employed with proportions would be about to 97% of the allo and about 15% to "3% of titanium carbide. I

The mixture is ball milled in a carbide-linedimill to about to 168 hours in a commercial solvent suchas 1 carbon tetrachloride. After drying, the mixtureisjthen briquetted or shaped at room temperature into ingots a pressures ranging from about 30 to t. s.'i.' (tons 'pe first at about 1100 to 1125 C. under a moderate vacuum; of the order of 50 microns Hg column. In the case of a 5 matrix of nickel-chromium alloy and a slip inhibitorof titanium carbide, strong out-gassing takes place at thi temperature due to a strong reaction between thenickel chromium alloy and the titanium carbide. 'A' small 'irigo 3" in:length and /2" square requires up to'6 hours jfo complete degassing by means of a mechanical vacuum pump, the exact time depending on the proportionaandig fineness of the nickel-chromium alloy and the titanium'car. bide powders. With the completion'of this first sinter ing stage, the ingot is ready for the second stage 'whic may either directly follow thefirst stage or which may to low an intermediate cooling under vacuum to room tern p'erature. The second stage has the purpose ofshrinkin and consolidating theingot to a density approaching as? is carried out at a temperature ranging from about 5 C; to 100 C. below the temperature of incipient fusion and; preferably from 25 ,C. to 100 C. below. The latter is about 1285 C. for a composition comprising about; 96%. by weight of the 8020 nickel-chromium alloy and 4% by weight titanium carbide. Itis about 1250 C. for a com chromium alloy and 10% by weight of titanium'carbide. The subatmospheric pressure during this'second phase of the treatment must be appreciably lower than th eifirst. It is preferred that it not exceed about 0.1 micron 11 column. The period of this second stage sintering-i's' de ,pendent on the size of the ingot: 4 hours being sufficie for a small ingot of 3inches in length and' /z inchsquare- 6% void spaceleft. w h u The thus-sinteredingot has excellent physicalprope a between the components).

ilies, namely,,amodul;us, of rupture, in the. order of 00,000 'p. s.1i a. yield point of 200,000.32, s. i., aniimpact resist- }"anee;at roomgtemperatureand at 1000 C. of over50 finch-pounds for, a-% .cross-sect ion as measured by; the

Micro Charpy Impact test. articlesi from thenovel material, such;as turbine blades, RQZZlQ an th i s. t ingot s hmh'o wo ke r exa pl a aho asina or or e s o u l t h been reducedi-n cross-sectionby at least 50% and pref- ..erably 90% f- 95%, until substantially all residual voids havebeen-eliminated andan optimum dispersion of the inhibitor phase'is obtained. Thematerialis then ready A for conventional metal working andfabricati-ng processes such as forging, rolling, cutting, trimming-weldingand b zin Further details concerning the invention become app arex t from the following examples.

.Example I ,About 96% by-weight of. substantially minus 325 mesh 80-.20 nickelrchromiu malloy powder is mixed with. about 4% by weight of substantially minus 2 micron high purity titanium carbide. i

The size-analysis of theI-nickel-chromium alloy powder .used as established by a microscopic count was as follows: Lessthan 2 -microns-about 16% ,AboutZ microns'to' '5 microns-about 44% ."About microns to.10 microns about 28% Abou ic ons. t 44 -m crq bc 1 Greater thanu44 microns about;0%

' The size analysis of -the titanium carbide I used is which :isgenera'lly much fineris as: follows: "Lessjthan 1'r nicron?about'95% Ab u 1 micro t -a q l m crqa wabo wt Maximum particle size about; *rnicrons Average particle size about"0.5 micron :The ;mixture was hall -;1r 1illed in a carbidelined mill s sin ic qbid b ll im q d-m wmp i s .Q tetrachloride. The procedure-used was-to 'fillitl'le mill acnethird ulliwith balls,- and. to fill the interstices between therballs. with the titanium carbide reinforced nickel chroi metal t-powder mixt re. padded ,to the half-way; mark in the mill. The mixture was -balbmilled forabout .one week (168 hours).

The powder was dried and then compacted into ztest specimens. The-testspecimens were iincheslong and inch wide. -Fifty, gr;ams of powder were used, and the -.compacting.pressure was;50:t. .s. i. The test specimens .obtained were. about 72% dense.

yIhe titanium carbide einforced metal powderspecirnens were ;sintered on a .berylliurn. oxide support in. an ultra high -vacuum .furnace. The specimen-and. support --.were,degassed,-at,pressures; fromrlOO. down to 5 0 microns ,,at .temperatures up to about.1O00-C. The furnace was ;,maintained at. 1125 .C.. until. the, pressure dropped below 20. microns. This degassing took. approximately six hours. .At ,this point, the high, vacuum ,diflusion pumps ..WGI'6 turned on and .a VZICHUI'ILOf better than.0.l micron was maintained throughout .theremainder of .thesintering op- ,eration. .The temperature was raised (always keeping .the vacuumbetter than 01 micron) until 31270C- was reached. This was .C.-less thanthe incipient fusion point of thealloy. Once the furnace hadreached 1270 C..and;.thevacuum was better than 0.1 micron, the speci- .men.-was..sintered:at these conditions for four hours." The furnace was: vacuum cooled.

The final ,density of the specimen was 8.15 g./ cc. (grams .per ,cubic 97.5%.. of the theoretical. density of the. composite (based .Qntheassumption that .there is substantially. no solubility The sintered material was then hot worked in accordance with the invention. to assistjn obtainingfull densification and an optimumdispersion. of ;.the .and recoveryinhibitor phase.

In order to produce useful Carbon tetrachloride wasv centimeter), which corresponds to 0.). The t'final density was .meter which corresponds to sity, assuming no solubility between the components. The

-E 2 cample II The method of *Exampled was employed except-that about 7% titanium carbide by weight all finer than 2 microns was added to about 93% by weight of the 8020 nickel-chromium alloy powder all finer than 40 microns and the finalsinteriug temperature was conducted at about .1255 C. (fusion point of this .alloy 1270 'The. .final density was 7.67 g./cc. which corresponds "to 9.4% of the=theoretical density, assuming no solubility between the components.

The sintered reinforced product was thenhot worked in accordance-with the invention,

.forexample ;.swaged, in order to obtainsubstantially full .densification and ;an.optimum dispersion of the slip inhibitor phase.

Example III C. (fusion point of-this alloy 1250 C.). The final density was. 7..4 g./ e c. whichcorresponds to 94% of the theoretical density (assuming substantially no solubility between the components). The sintered reinforced ,product was thereafter hot-worked for the reasons given in x mp a -II.

Example IV The method-of Example I was employedexcept that about :7% titanium ..car bide -;by weight, all liner .than .fl/z micron wasadded to about 93% by weight of 80 20 nickel chromium alloy powder, all finer than i-micror s, and the final sinteriag temperature was conducted at about 1255 C. (the fusion'point for this alloy is l270 7.70 grams percubic centi- 94.5% of thetheoretical den- --.sintered reinforcedproductwasthereafter hot-worked in about 510. t..s.-i.

.pressure. dropped. below 20 microns.

mainder of the sintering .cycle.

accordance with theinvention for the reasonsgiven in z'Examples L I and II.

Example 1 .V

.About=.90% byweight of substantially minus 325 mesh r60+32e6 cobalt-chromium-tungsten alloy powder was .mixed with .about'10% zbyweight of substantiallyminus :10 microns zirconium carbide. The mixture was dryabout 24-hours. The .powderwas compacted-into testspecimens. The test About 10 grams of powder were used and the compacting pressure was The test specimens obtained wereabout .dense. The zirconium carbide reinforced metal .powdenspecimens weresintered ona beryllium oxide support'insan ultra-high vacuum furnace. The specimens and .supports were degassed at pressuresless than SOLmicrons at'temperatures up .to approximately 1.000 C.

The furnacewas maintainedatabout 1000 C. untilthe Thisdegassing took approximately .4. hours. At:this point ..the high vacuum diffusion pumps .Wereturned onand a vacuum of better than 0.1 micron was maintained throughout the .re-

The .temperaturewas raised (always keeping thevacuum-better than 0.1 micron) untill-350" Cewas'reached. :This .isxabout 20;JC. less than the incipient fusion point. of the alloy. "Once the furnace had reached 1350" C. and the vacuumwvas less than 0.1-micron, the specimen wassintered atthese conditionsifon approximately 4; hours and the furnace vwas vacuum cooled. The final .densityof the specimen was 7.4 .grams per cubic ;entimeter -which corresponds to 90.0% ;of-;the

theoretical density of 1 thecomposite disregard inglimited solid solubility between. the components. However, 1 metallographic. examination revealed less than 2% perosity.

Thw a Fe as mam oke n aacat aacwithathe between examination revealed less than 2% porosity. The sintered' reinforced product was then hot-worked in accordance with the invention for the reasons given in Example- V.

invention to assist in obtaining full densification and an optimum dispersion of the slip and recovery inhibitor phase.

Example VI centimeter which corresponds to 90.4% of the theoretical density disregarding limited solid solubility between the components. However, 'metallographie"examination revealed less than 2% porosity. The sintered, reinforced product was then hot-worked in accordance with the I invention for the reasons given in Example V.

v I Example VII The method of Example VI was employed except that about 10% by weight of titanium boride (all minus 5 -microns) was used as the slip and recovery inhibitor phase. The sintering temperature for this composite was 1150 C. which is about 15 less than the fusion point of this alloy. The final density was 7.02 grams per cubic centimeter which corresponds to 90.5% of the theoretical density disregarding limited solid solubility the components. However, metallographic Example VIII The method of Example V was employed except that by weight of titanium nitride (all finer than 5 microns) was blended with about 90% by weight of an alloy which consisted of 20% cobalt, 20% chromium,

,2.3% titanium, 0.8 aluminum, and the balance nickel.

This alloy was substantially all minus 400 mesh. The final sintering temperature was conducted at approximately.1380 C., which is "about 20 C. less than the fusion point for this alloy. The final density was 7.70 grams per cubic centimeter which corresponds to 91.0% .of the theoretical density disregarding limited solid solubility between the components. However, metallographic' examination .revealed less than 2% porosity. The sintered reinforced product was then hot-worked in accordance with the invention, for the reasons given in Example V.

The strongest structure in the reinforced product of the invention is one in which the slip andrecovery inhibitor phase is extremely small, for example, whose average size is less than two microns and preferably even less than one micron, and in which the phase is uniformly distributed throughout the metal matrix in a substantially discontinuous random fashion. For optimummechanical properties, it is desired that the average spacing between the slip inhibitor phase should be less than one micron and preferably fall within the range of about 0.1 to 0.5 micron. If the average distance is greater than one micron the properties fall ofi appreciably and if the average distance is less than 0.1 micron the product may be brittle or the hard phase may dis- 'solve in subsequent heating treatments and lose its stability.

As illustrativeof the structures which are obtained with the reinforced product, reference is made to Figs. 1 and 2 of the drawing. Fig. 1 depicts the structure at '4000 times'rn'agnification of the reinforced product of the invention comprising about 7% by weight of titanium carbide distributed as an extremely small phase in a substantially discontinuous, random fashion through a matrix alloy of about nickel and 20% chromium -comprising about 93% by weight of the reinforced dispersed as fine particles as in the 8 a 7 product. Fig. 2 is the same magnification as Fig. 1 ex cept it depicts a structure containing about 10% byweight of the substantially insoluble titanium carbide slip. inhibitor phase distributed through the same matrix alloy.

In evaluating the capability of the reinforced product of the invention to sustain itself under stress at'elevat'ed temperatures, a short time high temperature tensile test is employed. The test comprises heating a tensile test specimen to an elevated temperature, say 1000" C., and determining its ultimate strength at that temperature in the conventional manner. In this way the'reinforced product ofv the invention can be compared to a similar product produced by conventional methods. Tests have shown an 80-20 nickel-chromiumalloy containing no TiC softens appreciably above 850 C. and generally has unsatisfactory resistanceto creep at 950? C. and high" temperatures. Even if the alloy contains elemental titanium and/or aluminum as age hardeners, the alloy softens due to overaging at 850 C. and higher and solution softens at 950 C. and higher when held at these temperatures for prolonged periods of time. In'either case the alloy suffers in its creep properties and may be unsatisfactory. However, when the alloy is reinforced by at least about 5% and up to about 20% by volume of the inhibitor material in accordance with the invention, e. g. with titanium. carbide, the alloy exhibits improved resistance to creep and is able to sustain itselfunder stress at a temperature range between 850 C. and 1050 C. for prolonged periods of time. When the alloy contains substantially less than 5% by volume of the slip and recovery inhibitor, the properties are not sufliciently improved in accordance with the invention. ,Likewise, when the alloy contains substantially more than 20% by volume of the inhibitor phase, the alloy loses its ductility and exhibits low resistance to impact. i i

As has been stated before, the novel results can" only be achieved by employing powder metallurgy as the procl essing method for producing the reinforced metalproduc V, of the invention. This enables the use of largeamounts of slip inhibitor compound material in amounts up to; about 20% by volume of the product *(or up, to about 15% by weight). Thus, a nickel-chromium reinforced product containing about 15% by weight offtitanium carbide would in effect contain about 12% by weightof. titanium and about 3% by weight of .carbon. If the same nickel-chromium product was produced by regular melting and casting procedures it would be necessary to add an equivalent of 12% titanium and 3% carbonlf Th alloy would be brittle and substantially unworkabl Furthermore, the titanium carbide in the cast product would be in the form of a substantially continuous den dritic phase and would not be homogeneous and even] case of 'therreinforced metal product of the invention. Such a cast material would also have a very lowresistance to impact. The product of the invention maintains a rather high resis ance to impact even when it contains large amounts of slip inhibitor material vprovided the slip inhibitor phase is uniformly dispersed throughout thematrix;

While it has been shown that substan'ti lly stable re i forced metal products of high strength can be produced from relatively soft nickel-chromium alloys of the 8020 nickel-chromium type alloy, it will be appreciated th at other typesof heat resistant alloys can'be reinforced g 1 including the age-hardenable nickel and cobalt-base alloys. Thus, the slip inhibitor can be used in conjunction with these alloys to further augment their .weight carrying capacity at elevated temperature. In other words, 'as the age hardening alloys lose their load carryingcapacity fat the high temperatures, the slip and recovery inhibit phase takes over and helps to sustain the strength of the alloy. i

Although the present invention has been describedin, conjunction with preferred embodiments, it is to be ,consisting of up to aboutj9 ni kaesaee'r .shigh-resistance to .zcreep atlelevated .=tempera-tures above I ;:800" 'Cna-nd-tupqtoiabout .1050 C. :for prolonged periods .iof timewhieh comprisesnmiformly mixing about :.to t by'lvolumepf-ta finely. adividedipowder ofaatslipaand .recoveryinhibiting compound .phaseahavinga particle-size .notl exceeding -:aboutzl.0amicrons selected from the-group consisting of -carbides,;b orides, rsilicides and nitrides of -;titanium,-. zirconium, colum-bium tantalum, vanadiumand thafnium, arrddisilicidesofi-molybdenum and tungsten, :with

a finely. dividedi heat a resistant. matrix; metal: powder not exceeding about 40 microns in size to make up substantially the ba-lanee saidhe'at resistant-matrixmetal comprising y weight abeutfii a o 3.Q% -..hr tn t rnup to about iron with substantially the remainder of, the matrix. metal "being .at least one metal selected jfrom ,the gr oup '7,Q%, cobalt, the sum ofthe nickeliand cobaltcontents being atleast about 40% by weight of the matrix metal composition, shaping said powder mixture to a coherent body, sintering the shaped body at a temperature of at least about 1100 C. to not greater than about 5 C. below the point of incipient fusion at a subatmospheric pressure not exceeding about 100 microns to produce a substantially dense body, hot working said sintered body to reduce its cross-sectional area at least about 50% to eliminate substantially the voids in said body and to effect optimum dispersion of said slip and recovery inhibiting phase, and then fabricating said hot worked body into a heat resistant article of manufacture, said fabricated article being characterized by a micro-structure having a substantially discontinuous and random dispersion of the finely divided slip and recovery inhibiting phase throughout the matrix of the heat resistant metal, the average distance between the finely divided phase being not greater than about one micron.

2. A method for reinforcing heat resistant metal prod ucts capable of sustaining high strength properties and high resistance to creep at elevated temperatures above 800 C. and up to about 1050 C. for prolonged periods of time which comprises uniformly mixing about 5% to 20% by volume of a finely divided powder of a slip and recovery inhibiting compound phase having a particle size not exceeding about 2 microns selected from the group consisting of carbides, borides, silicides and nitrides of titanium, zirconium, columbium, tantalum, vanadium, and hafnium, and disilicides of molybdenum and tungsten, with a finely divided heat resistant matrix metal powder not exceeding about 5 microns in size to make up substantially the balance, said heat resistant matrix metal comprising by weight about 5% to chromium, up to about 25% iron with substantially the remainder of the matrix metal being at least one metal selected from the group consisting of up to about 90% nickel and up to about 70% cobalt, the sum of the nickel and cobalt contents being at least about by weight of the matrix metal composition, shaping said powder mixture to a coherent body, sintering the shaped body first at a temperature of about 1100 C. to 1125 C. at a subatmospheric pressure not exceeding about microns of mercury column followed by a second sintering at a temperature of 5 C. to 100 C. below the point of incipient fusion at a subatrnospheric pressure not exceeding about 0.1 micron of mercury column to produce a substantially dense body, hot working said sintered body to reduce its cross-sectional area to at least about 50% to eliminate substantially the voids in said body and to effect optimum kel ..and up, to, about I adispersionaof said;slip andlrecoverytinhibiting phase and tsistant .tmetal, tithe ..average..-idistance between the .finely .zdivided phase. being not greater than. about one micron.

:3. Amethod forireinforcing .heatresistahtmetahproducts capable- .of sustaining high strength properties .and high resistance .itO .creep at. elevated:temperatnres; above about 800 C. and up to about 1050 C. for prolonged .periqdsof time..which comprises. uniformlymixing about 1.62% a .to-y2.0% 1 by yolume of a-rfinely. divided .powder.. of a .slipx and .recoyery inhibitingcompound phase shaving a particle size-notlexceedingaabout 1 mic r.on.=selected from the group consisting .of carbides, borides, .-silicides .and vnitridesbf titanium, zirconium, columbium, tantalum, t-vanadium,sands hafimum and gdisilicigiesltofrrnolybdenurn Land: tungstemawith sarfinely :divided: heat. resistant matrix nmetalspowder ,not .exceedingtabout: 5 microns in size l .to ;-make.-unsubstantiallw :the balance, said heat. resistant mar-HiX metal;comprisingnbysweight ot=about 5% .to-30% 'rchromium .up i .to .about*r25;% r iron .with. substantially. the

' perature of about 25 C. to 100 C. below the point of incipient fusion at a subatmospheric pressure not exceeding about 0.1 micron of mercury column to produce a substantially dense body, hot working said sintered body to reduce its cross-sectional area to at least about to eliminate substantially the voids in said body and to effect optimum dispersion of said slip and recovery inhibiting phase, and then fabricating said hot worked body into a heat resistant article of manufacture, said fabricated article being characterized by micro-structure having a substantially discontinuous and random dispersion of the finely divided slip and recovery inhibiting phase throughout the matrix of the heat resistant metal, the average distance between the finely divided phase being of the order of about 0.1 to 0.5, micron.

4. A method for reinforcing heat resistant metal products capable of sustaining high strength properties and high resistance to creep at elevated temperatures above 800 C. and up to about 1050 C. which comprises uniformly mixing about 5% to 20% by volume of a finely divided powder of a slip and recovery inhibiting compound phase comprising titanium carbide having a particle size not exceeding about 1 micron with a finely divided heat resistant matrix metal powder not exceeding about 5 microns in size to make up substantially the balance, said heat resistant matrix metal comprising by weight about 5% to 30% chromium, up to about 25% iron with substantially the remainder of the matrix metal being at least one metal selected from the group consisting of up to about 90% nickel and up to about 70% cobalt, the sum of the nickel and cobalt contents being at least about 50% by weight of the matrix metal composition, shaping said powder mixture to a coherent body in a mold under a pressure of about 30 to 150 t. s. i., sintering the shaped body first at a temperature of about 1100 C. to 1125 C. at a subatrnospheric pressure not exceeding about 50 microns of mercury column followed by a second sintering at a temperature of about 25 C. to C. below the incipient point of fusion at a subatmospheric pressure not exceeding about 0.1 micron to produce a substantially dense body, hot working said sintered body to reduce its cross-sectional area to at least about 90% to into a heat resistant article of manufacture, said fabricated article being characterized by microstructure having a substantially discontinuous and random dispersion of the finely divided slip and recovery inhibiting phase comprising titanium carbide throughout the matrix of the heat resistant metal, the average distance between the finely divided phase being of the order of about 0.1 to 0.5 micron.

5. A method for reinforcing heat resistant metal products capable of sustaining high strength properties and high resistance to creep at elevated temperatures above 800 C. and upto 1050 C. for prolonged'periods of time which comprises uniformly mixing about to by volume of a finely divided powder of a slip and recovery inhibiting compound phase selected from the group consisting of carbides, boride's, silicides, and ni-' trides of titanium, zirconium, columbium, tantalum, vanadium and hafnium, and disilicides of molybdenum and tungsten, with a finely divided heat-resistant matrix metal powder to make up substantially the balance, said heat resistant matrix metal comprising by weight about 5% to chromium, u'pto about 25% iron with substantially' the remainder of the matrix metal being at 't'ure, said fabricated article being characterized by a nu'crostructure having a substantially discontinuous and microns vto produce a substantially dense body, hot work- .ing said sintered body to reduce its cross-sectional area atv yand'recovery inhibiting phase, and then fabricating said 12 V 7 least one metal selected from the group consisting ofiup to about 90% nickel and up to about 70% cobalt, the j sum of the nickel and cobalt contents being at least about 40% by weight of the matrix metal composition, shaping said powder mixture to a coherent body, 'sintering the shaped body at'a temperatureof at least about 1100 C. at a subatmospheric pressure not exceeding'aboult' 100 least about to eliminate substantially the voids in said body and to effect optimum dispersion of said slip hot worked body into a heat resistant article of manufacrandom dispersion of the finely divided slip and recovery inhibiting phase throughout the matrix of the heat resistant metal, the average distance between the finely dividedphase being not greater than about one micron.

:, References Cited in the file of this patent UNITED STATES PATENTS 2,106,162 Balke Ian. 25, 1938 2,174,025 Wise et al Sept. 26,1939' 2,580,171 Hagglund et al Dec. 25, 1951; 2,686,118

'Cavanagh Aug. 10, 1 954- 

1. A METHOD FOR REINFORCING HEAT RESISTANT METAL PRODUCTS CAPABLE OF SUSTAINING HEAT STRENGTH PROPERTIES AND HIGH RESISTANCE TO CREEP AT ELEVATED TEMPERATURES ABOVE 800*C. AND UP TO ABOUT 1050*C. FOR PROLONGED PERIODS OF TIME WHICH COMPRISES UNIFORMLY MIXING ABOUT 5% TO 20% BY VOLUME OF A FINELY DIVIDED POWDER OF A SLIP AND RECOVERY INHIBITING COMPOUND PHASE HAVING A PARTICLE SIZE NOT EXCEEDING ABOUT 10 MICRONS SELECTED FROM THE GROUP CONSISTING OF CARBIDES, BORIDES, SILICIDES AND NITRIDES OF TITANIUM, ZIRCONIUM, COLUMBIUM, TANTALUM, VANADIUM AND HAFNIUM, AND DISILICIDES OF MOLYBDENUM AND TUNGSTEN, WITH A FINELY DIVIDED HEAT RESISTANT MATRIX METAL POWDER NOT EXCEEDING ABOUT 40 MICRONS IN SIZE TO MAKE UP SUBSTANTIALLY THE BALANCE, SAID HEAT RESISTANT MATRIX METAL COMPRISING BY WEIGHT ABOUT 5% TO 30% CHROMIUM, UP TO ABOUT 25% IRON WITH SUBSTANTIALLY THE REMAINDER OF THE MATRIX METAL BEING AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF UP TO ABOUT 90% NICKEL AND UP TO ABOUT 70% COBALT, THE SUM OF THE NICKEL AND COBALT CONTENTS BEING AT LEAST ABOUT 40% BY WEIGHT OF THE MATRIX METAL COMPOSITION, SHAPING SAID POWDER MIXTURE TO A COHERENT BODY, SINTERING THE SHAPED BODY AT A TEMPERATURE OF AT LEAST ABOUT 1100*C. TO NOT GREATER THAN ABOUT 5*C. BELOW THE POINT OF INCIPIENT FUSION AT A SUBATMOSPHERIC PRESSURE NOT EXCEEDING ABOUT 100 MICRONS TO PRODUCE A SUBSTANTIALLY DENSE BODY, HOT WORKING SAID SINTERED BODY TO REDUCE ITS CROSS-SECTIONAL AREA AT LEAST ABOUT 50% TO ELIMINATE SUBSTANTIALLY THE VOIDS IN SAID BODY AND TO EFFECT OPTIMUM DISPERSION OF SAID SLIP AND RECOVERY INHIBITING PHASE, AND THEN FABRICATING SAID HOT WORKED BODY INTO A HEAT RESISTANT ARTICLE OF MANUFACTURE, SAID FABRICATED ARTICLE BEING CHARACTERIZED BY A MICRO-STRUCTURE HAVING A SUBSTANTIALLY DISCONTINUOUS AND RANDOM DISPERSION OF THE FINELY DIVIDED SLIP AND RECOVERY INHIBITING PHASE THROUGHOUT THE MATRIX OF THE HEAT RESISTANT METAL, THE AVERAGE DISTANCE BETWEEN THE FINELY DIVIDED PHASE BEING NOT GREATER THAN ABOUT ONE MICRON. 